feat!: merge chart properties

[vincent-onebrief]

Description

The charts key supports merging, but doesn't support merging all properties. This isn't covered by the documentation well. Being able to override these properties allows for more complex CI testing where the zarf package needs to reference a derivative chart specific to the PR (as an example).

Related Issue

Checklist before merging

• Test, docs, adr added or updated as needed
• Contributor Guide Steps followed

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Files with missing lines	Coverage Δ
src/pkg/packager/load/import.go	51.16% <100.00%> (+2.88%)	⬆️

... and 1 file with indirect coverage changes

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[AustinAbro321]

Generally I agree with this change. It doesn't really make sense to specify the url and version in your base zarf.yaml and for it to be impossible to have an effect. Have a minor the test / directory name

[AustinAbro321]

LGTM. Now if your base zarf.yaml defines a chart.url or chart.version it will not be overwritten. While there would be no reason to specify the chart.url or chart.version before in this situation, I added a ! to denote that this is a breaking change if they were.

[brandtkeller]

LGTM - appreciative of this gap being addressed.